Knowledge of the location of a vehicle relative to its environment is crucial, particularly for autonomous robots. Presently there are a number of distinct systems which utilize internal or external reference systems to provide a known orientation to the outside world. This orientation is crucial not only for navigation but also for identifying the direction of detectable events such as an intruder or a fire.
Internal reference is typically provided by inertial reference utilizing a gyroscope. Accurate gyroscopes, particularly digitally readable ones, are quite expensive and are relatively delicate.
Internal reference can also be provided by dead reckoning. Encoders on the drive system record the distance travelled by the wheels or tracks of the robot. This technique, also known as odometry, further includes steering encoders to record changes in orientation.
Other systems model the surrounding environment by reducing the environment to geometric features. The robot matches the perceived geometric model with the expected model and correlates them to determine its error in position. The environment is typically modelled as a series of line segments representing surface features, or as a grid representing the probability of presence or absence of obstructions within particular locations.
Yet other systems rely on a number of markers placed in the environment. A landmark system utilizes markers placed on walls along a path to denote the distance travelled.
Some other systems calibrate positions at predetermined locations, or nodes, where a number of markers are installed to permit triangulation. One system uses three infrared beacons to triangulate position. Triangulation can also be accomplished using other forms of energy such as radio waves.
Another system triangulates its position using a rotating laser. The laser beam reflects off corner reflectors at designated locations. The system determines the angles among the reflectors to triangulate its position.
Some robots are equipped with a drive system which drives and steers all wheels simultaneously. This locomotion system is known as a synchro-drive. The azimuthal angle of the base or body of a robot equipped with a synchro-drive remains relatively stationary relative to the environment. Robots are typically equipped with synchro-drive when great maneuverability is desired, since synchro-drive enables the vehicle to turn on its own axis. One such robot is guided by remote control.
Navigation systems must take into account drift of the vehicle over time. Drift results in a lateral deviation from the direction of travel and may also result in a change in heading. In addition, for a robot with synchro-drive, the azimuthal angle of the body does not remain absolutely stationary but rotates slightly over time due to precession. Precession is caused by friction between the wheels and the floor which exerts torque on the chassis, resulting in a change of azimuthal orientation opposite that of the steering direction.